Refactor Metrics to allow different user selections

[Konohana0608]

To ensure versatility and the future idea to allow users to add custom metrics, the TIP code base needs refactoring. We will build an object that functions as a metrics database to hold all existing metrics. These can then be added or removed in the frontend. For now, we will only allow predefined metrics, but later this should be opened up to allow user-defined custom metrics. These could be in the form of a Mathematica script, which is parsed using Sympy.

To Dos:

• Create a new Metrics Base Model
• Implement the Metrics "Database" Class (provide query, loading ,and saving)
• Adapt MetricsDefiner: Interface for showing the selected metrics, which can be removed, and an interface to add metrics from a list of all available metrics.
• Adapt the current code base to work with these changes.